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City dwellers compete with the din of traffic to be heard. And it’s not just urban humans. Sparrows living in San Francisco's Presidio district actually tweet their tunes in a higher register than they did in the past, to be heard over the rumble of cars on the nearby Golden Gate Bridge. So says a study in the journal Animal Behavior.
城市居民往往受困于喧嚣的交通噪音。其实不堪其扰的不只是城市居民。旧金山要塞区麻雀的鸣叫声实际上比它们以往任何时候的叫声都要更高——这样人们才能在驶过附近金门大桥的汽车隆隆声中听到它们的鸣叫。这项研究刊登在《动物行为》杂志上。
Researchers compared white-crowned sparrow songs recorded in 1969 and 2005. Over that time span, ambient noise levels went up. And the bird calls were essentially the same—but the more recent one was higher inpitch. The change presumably allows the song to better penetrate the traffic noise.
研究人员比较了白冠麻雀1969年至2005年的叫声记录。在这段时间内，环境噪声分贝直线上升。它们的叫声基本上还是相同的，但最近音高明显上升了。据推测，只有这样它们的叫声才能穿透交通噪音。
The modern calls carry more weight with the birds too. Because when male sparrows heard the 2005 recordings played back in their territory, they responded more aggressively—swooping in on the speaker with a “get outta here" chirp and flapping their wings at the suspected intruder.
现代鸟类的叫声显示它们承载着更多的压力。因为当雄性麻雀听到2005年它们的叫声录音时，它们的反应更具有侵略性——它们冲着扬声器俯冲并发出“离开这里”的警告，而且还用翅膀扑打疑似入侵者。
The researchers say most species simply can't handle the noise and cramped habitats of the city, and head to the country. The adaptable sparrow, however, simply changed its tune.
研究人员说，大多数物种完全无法应对噪音对它们的影响，也无法适应拥挤的城市栖息地，最终只能逃到乡下去。然而，适应了这种城市噪音的麻雀则完全改变了它们鸣叫声。
